FIG. 1 illustrates a schematic view of a structure of an integrated circuit 1 for contactless operation. This circuit is of a type mounted in contactless chip cards, electronic labels, and other portable devices that work without contact. The circuit 1 comprises an input stage 10, a rectifier circuit 15, a demodulator circuit 20, a modulator circuit 21, and a central processor unit (CPU) 22. The CPU 22 comprises, for example, a microprocessor and an EEPROM. The input stage 10 is a parallel resonant circuit comprising an input capacitance C.sub.in integrated into the silicon, and at least one antenna coil 11 connected to the terminals of the capacitance C.sub.in by connection pads 12. The resonant frequency or natural frequency Fp of the input stage 10 is governed by a regulation, and is generally equal to 13.56 MHz.
When the integrated circuit 1 is subjected to an alternating magnetic field Fld with a frequency Fp, an alternating voltage Vac is received in the antenna coil 11 by electromagnetic induction. The alternating magnetic field Fld is emitted, for example, by a station 30 fitted with a coil 31. This voltage Vac could reach 40 volts and is converted by the rectifier circuit 15 into a direct voltage Vcc for the supply of the integrated circuit. Furthermore, the voltage Vac is demodulated by the circuit 20 for the reception of data DTIN. For the transmission of data DTOUT to the station 30, the voltage Vac is modulated by the circuit 21 according to the standard technique of load modulation. Naturally, various other standard techniques may be implemented for the reception or transmission of data. For example, techniques using infrared, radioelectric or other signals are acceptable. In every case, however, activation of the integrated circuit 1 by induction requires that the input stage 10 be excited by a magnetic field.
Like other integrated circuits, the contactless circuits are manufactured in batches on a silicon wafer. However, at this stage of manufacture, the input stage 10 is not completed and does not include the antenna coil 11. It is only after cutting of the wafer that the antenna coil 11 is connected to the capacitance C.sub.in before the input stage 10 becomes operational. After cutting the wafer, each integrated circuit is individually mounted on a support, such as a plastic card. The integrated circuits are then activated by a magnetic field and electrically tested to eliminate those that are defective.
The manufacturing output values for integrated circuits are mediocre, and a wafer generally contains various circuits that are defective. The sorting out of such defective circuits requires their assembly on supports and their connection to antenna coils. This effort leads to a waste of labor and raw materials which increases the cost of the portable contactless devices. Thus, the present invention proposes to implement a method of testing on wafer to assess the electrical characteristics of contactless circuits before they are cut out from the silicon wafers.
The implementation of an on wafer testing method requires application to the input stage of each circuit a test voltage simulating the alternating voltage Vac received by induction. This test voltage must be about 20 to 40 volts peak-to-peak with a frequency of about 13.56 MHz. Typically, the most efficient HF signal generators available in the market deliver voltages that do not exceed a few volts. They cannot be used to activate integrated circuits working by induction.